The present invention relates in general to an apparatus such as a camera and an image reading apparatus in which is used a film provided with perforations, and in particular, to a perforation detection device provided for them. The present invention relates more particularly to a device for detecting perforations of a film by an intermittent contact of two contact pieces that are arranged at the front and the rear of a path in which the perforations of the film advance.
Conventionally, as a perforation detection device for a camera, there have been adopted a sprocket type, a photo-interrupter type, a contact piece type and so forth. The perforation detection device of the sprocket type is to control film feed by detecting the number of perforations that have passed from the amount of rotation of a sprocket that is meshed with a number of perforations formed continuously at short pitches along a longer side edge of a 35-mm film. The photo-interrupter type is to detect the passage of the perforations by means of a photo-interrupter (or an optical sensor similar to it) arranged on the path in which the perforations advance. The contact piece type is to detect the perforations of a film by an intermittent contact of two contact pieces that are arranged in a path in which the perforations of the film advance and put in pressure contact with each other with interposition of the film as the perforations pass in a film feeding stage. In this case, one of the contact pieces has its tip end portion bent in a convex form so that it comes in contact with the other contact piece through a perforation, constituting a detection section.
Among the aforementioned types, the sprocket type can easily control one-frame feed of the film based on the amount of rotation of the sprocket since the sprocket continuously rotates while being meshed with the perforations in the case of the 35-mm film in which a number of perforations are formed at short pitches along the longer side edge of the film. However, in the case of a new-standard film in which two perforations are formed per frame and which has started to be used lately, it can be considered that the sprocket construction and the mechanism control will be complicated because the perforation interval is not uniform. The photo-interrupter type has the disadvantage that the cost of the photo-interrupter itself is expensive as compared with the other types and a supplementary construction such as a control circuit therefor costs much.
In contrast to this, the contact piece type has the advantage that it is relatively inexpensive and it has an excellent adaptivity to different film standards because it can relatively easily cope with a change of the perforation interval. However, the film advances while in particular the detection section of the contact piece is put in pressure contact with the film surface. Therefore, it is possible that the contact pieces will be a resistance to the film feed or injure the film.
In view of the above, it can be considered that the perforation detection device of the contact piece type can be provided as a relatively low-cost detection device in a camera regardless of the film standard if the possibility that the contact pieces will be a resistance to the film feed or injure the film is reduced.